With the latest Senate Democrat’s retirement announcement, there are now three open Democratic seats in highly competitive states.

That’s half the total number of seats Senate Republicans must net to win the majority.

South Dakota Sen. Tim Johnson announced Tuesday that he will not seek re-election, joining Sens. Jay Rockefeller of West Virginia and Tom Harkin of Iowa in retirement after 2014. Their departures mark the three most competitive seats of the five Democratic retirements so far this year and offer avenues for the GOP to cut into the majority.

Add in five Democratic incumbents running in states President Barack Obama lost, and the GOP is positioned to pick up a significant number of seats in 2014.

National Republican Senatorial Committee spokesman Brad Dayspring said the “map and conditions have been favorable to Republicans,” but the party must now take advantage of that by recruiting strong candidates and equipping them with well-trained staff.

“To use a sports analogy, we have home field advantage, the weather conditions are in our favor, but you’ve still got to put the best team out on the field and you’ve still got to execute the plays,” Dayspring said.

Of course, Republicans were well-positioned early in the 2012 cycle as well, but suffered a net loss of two seats on Election Day.

Picking up the six Democratic seats needed for the majority remains an arduous feat. To get there, the party would have to match its Election Day output in the wave election cycle of 2010 — the previous midterm. Republicans won six seats that November, plus the Massachusetts special Senate election earlier in the year.

It’s too early to know what the political atmospherics will be headed into the fall of next year.

For now, Democrats remain optimistic they can recruit candidates to hold their open seats and that most of the party’s vulnerable incumbents will be able to hang on in Republican-leaning states. They certainly did last year in Montana and Missouri, and the party held an open seat in North Dakota, where Obama lost by about 20 points.

“D.C. Republicans seem overconfident once again, even though the math is much more difficult for them this cycle and their influence with the conservative base has waned,” said Matt Canter, deputy executive director for the Democratic Senatorial Campaign Committee. “The Republican establishment claims they are going to do a better job managing the tea party and handpicking mainstream candidates that can win, but they don’t seem to have any good strategy to do that.”

On the surface, the numbers are harrowing for Democrats, who have a limited number of offensive opportunities and must defend 21 of the 35 seats — including special elections — up this cycle. That includes seven states Obama lost and a total of at least nine potentially competitive, Democratic-held seats.

South Dakota and West Virginia are no doubt two of the best pickup opportunities for Republicans, who already have top recruits in place. Former South Dakota Gov. Mike Rounds and West Virginia Rep. Shelley Moore Capito announced their bids shortly after the elections in November.

While still recruiting in West Virginia, Democrats already have potential candidates in South Dakota in former Rep. Stephanie Herseth Sandlin and U.S. Attorney Brendan Johnson, the senator’s son.

Johnson said during his retirement announcement that it was no secret he had spoken with his son about running for Senate. But later, in a news conference, Johnson noted that he has no plans to be active during the race and is busy enough with his duties in the Senate.

In Iowa, Democratic Rep. Bruce Braley immediately announced his candidacy after Harkin retired. Democrats like their chances in the Hawkeye State should GOP Rep. Steve King, a conservative who top Republican strategists worry is too undisciplined to win statewide, decides to run. King told CQ Roll Call recently that he is still undecided.

The Democrats’ most vulnerable incumbents are, at this point in the cycle, at least an even bet for re-election. Many of them — including Alaska’s Mark Begich, North Carolina’s Kay Hagan, Louisiana’s Mary L. Landrieu and Arkansas’ Mark Pryor — are still awaiting major GOP challengers.

Along with Capito and Rounds, Republicans also have candidates to take on Democratic Sen. Max Baucus of Montana, including former state Sen. Corey Stapleton.

Democrats’ optimism stems in part from the GOP’s recent track record of nominating weak general election challengers. In 2012, top Senate GOP recruits ran lackluster campaigns. What’s more, in the past two cycles, a handful of long-shot conservatives proved unable to adequately compete for a general electorate.

A total of seven senators, including five Democrats, have announced their retirements so far this year, including Johnson, Harkin and Rockefeller. The remaining four are Democratic Sens. Carl Levin of Michigan and Frank R. Lautenberg of New Jersey and Republican Sens. Saxby Chambliss of Georgia and Mike Johanns of Nebraska.

Given those four states’ recent electoral trends, both parties start out favored to hold their own open seats. But the Levin and Chambliss seats could eventually become more competitive based on whom the parties recruit and which candidates make it out of what are likely to be crowded GOP primaries.